: Indoor allergens including molds and bacterial byproducts (e.g., endotoxin) have the potential to act as protective agents versus allergens capable of sensitizing and causing allergies and asthma. This project will demonstrate proof of concept through a prospective investigation of exposure to common indoor allergens and microorganisms in the home. A unique system of prolonged environmental exposure assessment which correlates clinical symptoms, objective changes in lung function and allergen sensitization with environmental exposure will be used to measure the effectiveness of a novel ultraviolet (UV) air remediation system. Preliminary evidence indicates that the CREON2000 Photonic UV system disinfects the air it treats by killing mold spores and bacteria. Twenty households with a mild-persistent allergic asthmatic child between the ages of 6 and 12 will be selected to participate in this six-month double blind, placebo-controlled crossover trial. Initially half of the homes will have a CREON2000 system and the other half a sham system installed into their respective duct works. At 10 weeks, these systems will be exchanged. Prior to enrollment, allergic sensitization of participants will be confirmed by skin prick testing to perennial allergens (at least one indoor mold and one other perennial indoor allergen) and airway limitation by objective pulmonary function testing (a 12-15% change in forced expiratory volume in one second (FEV-1). Baseline assessment of participants will include a thorough home and school environmental history, disease specific and non-specific quality of life questionnaires and physical examination. A two-week, prolonged environmental exposure assessment will be performed at baseline, 8 weeks and 22 weeks. Environmental exposure assessment will include air and settled dust samples to analyze allergens (dust mite, cat, dog, cockroach and Aspergillus, Penicillium, Cladosporium and Alternaria mold spores) and bacterial and endotoxin levels in the child's bedroom. Outdoor air samples will be collected simultaneously. HOBO electronic data collectors (Scott Technical Instruments Ltd.) will be used to monitor environmental conditions throughout the study. Upon successful completion of this study, the next steps will include a larger prospective clinical trial to investigate long-term (more than12 months) health outcomes of asthmatic children after prolonged use of the CREON2000 in the home and conduct more detailed investigation of whether and how UV radiation alters protein allergenicity.